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Ulf-G. Meißner

Publications and source records attributed to Ulf-G. Meißner.

At least 469 records · Page 26Linked to original sources
arXiv2007

Dbar-N interaction from meson-exchange and quark-gluon dynamics

We investigate the Dbar-N interaction at low energies using a meson-exchange model supplemented with a short-distance contribution from one-gluon-exchange. The model is developed in close analogy to the meson-exchange KN interaction of the Juelich group utilizing SU(4) symmetry constraints. The main ingredients of the interaction are provided by vector meson (rho, omega) exchange and higher-order box diagrams involving D*N, DΔ, and D*Δintermediate states. The short range part is assumed to receive additional contributions from genuine quark-gluon processes. The predicted cross sections for Dbar-N for excess energies up to 150 MeV are of the same order of magnitude as those for KN but with average values of around 20 mb, roughly a factor two larger than for the latter system. It is found that the omega-exchange plays a very important role. Its interference pattern with the rho-exchange, which is basically fixed by the assumed SU(4) symmetry, clearly determines the qualitative features of the Dbar-N interaction -- very similiar to what happens also for the KN system.

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arXiv2007

Nuclear forces with Delta-excitations up to next-to-next-to-leading order I: peripheral nucleon-nucleon waves

We study the two-nucleon force at next-to-next-to-leading order in a chiral effective field theory with explicit Delta degrees of freedom. Fixing the appearing low-energy constants from a next-to-leading order calculation of pion-nucleon threshold parameters, we find an improved convergence of most peripheral nucleon-nucleon phases compared to the theory with pions and nucleons only. In the delta-full theory, the next-to-leading order corrections are dominant in most partial waves considered.

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arXiv2007

Neutron-proton mass difference in nuclear matter

Isospin-breaking effects in nuclear matter are studied in the framework of a medium-modified Skyrme model. The proposed effective Lagrangian incorporates both the medium influence of the surrounding nuclear environment on the single nucleon properties and an explicit isospin-breaking effect in the mesonic sector. The approach predicts that the neutron-proton mass difference decreases in isospin-symmetric nuclear matter but by a very small amount only.

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arXiv2007

The Delta-resonance in a finite volume

We study the extraction of Delta-resonance parameters from lattice data for small quark masses, corresponding to the case of an unstable Delta. To this end, we calculate the spectrum of the correlator of two Delta-fields in a finite Euclidian box up-to-and-including O(epsilon^3) in the small scale expansion using infrared regularization. On the basis of our numerical study, we argue that the extraction of the parameters of the Delta-resonance (in particular, of the mass and the pion-nucleon-delta coupling constant) from the measured volume dependence of the lowest energy levels should be feasible.

hep-lat↗
arXiv2007

The hyperon-nucleon interaction: conventional versus effective field theory approach

Hyperon-nucleon interactions are presented that are derived either in the conventional meson-exchange picture or within leading order chiral effective field theory. The chiral potential consists of one-pseudoscalar-meson exchanges and non-derivative four-baryon contact terms. With regard to meson-exchange hyperon-nucleon models we focus on the new potential of the Juelich group, whose most salient feature is that the contributions in the scalar--isoscalar (σ) and vector--isovector (ρ) exchange channels are constrained by a microscopic model of correlated ππand KKbar exchange.

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arXiv2007

The pp -> K^+Sigma^+n cross section from missing mass spectra

We utilize existing inclusive data on K^+ meson momentum spectra of the reaction pp -> K^+X at T_p = 2.3 - 2.85 GeV to deduce total cross sections for pp -> K^+Σ^+n. The method used to extract those cross sections is explained and discussed in detail. Our result for T_p = 2.85 GeV is consistent with the data point from a direct measurement at the same beam energy. The cross section obtained for T_p = 2.3 GeV is with 13.7\pm2.3 μb considerably smaller than the value found in a recent experiment by the COSY-11 Collaboration at a somewhat lower beam energy, indicating that the pp -> K^+Σ^+n reaction cross section could exhibit a rather unusual energy dependence.

hep-ph↗
arXiv2006

T-odd correlations in radiative K_l3^+ decays and chiral perturbation theory

The charged kaon decay channel K_l3gamma^+ allows for studies of direct CP violation, possibly due to non-standard mechanisms, with the help of T-odd correlation variables. In order to be able to extract a CP-violating signal from experiment, it is necessary to understand all possible standard model phases that also produce T-odd asymmetries. We complement earlier studies by considering strong interaction phases in hadronic structure functions that appear at higher orders in chiral perturbation theory, and compare our findings to other potential sources of asymmetries.

hep-ph↗
arXiv2006

Lattice Simulations for Light Nuclei: Chiral Effective Field Theory at Leading Order

We discuss lattice simulations of light nuclei at leading order in chiral effective field theory. Using lattice pion fields and auxiliary fields, we include the physics of instantaneous one-pion exchange and the leading-order S-wave contact interactions. We also consider higher-derivative contact interactions which adjust the S-wave scattering amplitude at higher momenta. By construction our lattice path integral is positive definite in the limit of exact Wigner SU(4) symmetry for any even number of nucleons. This SU(4) positivity and the approximate SU(4) symmetry of the low-energy interactions play an important role in suppressing sign and phase oscillations in Monte Carlo simulations. We assess the computational scaling of the lattice algorithm for light nuclei with up to eight nucleons and analyze in detail calculations of the deuteron, triton, and helium-4.

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arXiv2006

Chiral perturbation theory

We give a brief introduction to chiral perturbation theory in its various settings. We discuss some applications of recent interest including chiral extrapolations for lattice gauge theory.

hep-ph↗
arXiv2006

Lattice QCD, Chiral Perturbation Theory and Hadron Phenomenology

These are the proceedings of the workshop on ``Lattice QCD, Chiral Perturbation Theory and Hadron Phenomenology'' held at the European Centre for Theoretical Studies in Nuclear Physics and Related Areas from October 2 to 6, 2006. The workshop concentrated on bringing together researchers working in lattice QCD and chiral perturbation theory with the aim of improving our understanding how hadron properties can be calculated and analyzed from first principles. Included are a short contribution per talk.

hep-ph↗
arXiv2006

KKbar photoproduction from protons

We study the contribution of the Drell mechanism driven by K^+ and K^- exchange to the reaction gamma N -> KKbar N. Our calculation implements the full KN and KbarN reaction amplitudes in the form of partial wave amplitudes taken from a meson-exchange model (KN) and a partial wave analysis (KbarN), respectively. Comparing our results to data of the LAMP2 collaboration we observe that the Drell mechanism alone cannot describe the large Lambda(1520) photoproduction rate observed experimentally. We argue that the discrepancy could be due to significant contributions from K*-meson exchange with subsequent excitation of the Lambda(1520) resonance. After adding such contributions to our model a good agreement of the LAMP2 experiment is achieved. When applying the same model to the recent SAPHIR data we find an excellent description of the K^+p spectrum and can determine the parameters of the Lambda(1600) P01 resonance, M_R = 1617 +/- 2 MeV and Gamma_R = 117 +/- 4 MeV, from the K^-p mass distribution.

hep-ph↗
arXiv2006

Improved Analysis of J/psi Decays into a Vector Meson and Two Pseudoscalars

Recently, the BES collaboration has published an extensive partial wave analysis of experimental data on J/psi -> phi pi+pi-, J/psi -> omega pi+pi-, J/psi -> phi K+K- and J/psi -> omega K+K-. These new results are analyzed here, with full account of detection efficiencies, in the framework of a chiral unitary description with coupled-channel final state interactions between pi-pi and K-bar K pairs. The emission of a dimeson pair is described in terms of the strange and nonstrange scalar form factors of the pion and the kaon, which include the final state interaction and are constrained by unitarity and by matching to the next-to-leading-order chiral expressions. This procedure allows for a calculation of the S-wave component of the dimeson spectrum including the f_0(980) resonance, and for an estimation of the low-energy constants of Chiral Perturbation Theory, in particular the large N_c suppressed constants L_4^r and L_6^r. The decays in question are also sensitive to physics associated with OZI violation in the 0++ channel. It is found that the S-wave contributions to phi pi+pi-, phi K+K- and omega pi+pi- given by the BES partial-wave analysis may be very well fitted up to a dimeson center-of-mass energy of ~1.2 GeV, for a large and positive value of L_4^r and a value of L_6^r compatible with zero. An accurate determination of the amount of OZI violation in the J/psi -> phi pi+pi- decay is achieved, and the S-wave contribution to omega K+K- near threshold is predicted.

hep-ph↗
arXiv2006

Kaon-Deuteron Scattering at Low Energies

We review the experimental information on the K^+d reaction for K-meson momenta below 800 MeV/c. The data are analysed within the single scattering impulse approximation -- utilizing the Juelich kaon-nucleon model -- that allows to take into account effects due to the Fermi motion of the nucleons in the deuteron and the final three-body kinematics for the break-up and charge exchange reaction. We discuss the consistency between the data available for the K^+d -> K^+np, K^+d -> K^0pp and K^+d -> K^+d reactions and the calculations based on the spectator model formalism.

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